When most people think of synthesizers they think of all-in-one instruments that are programmed by pushing buttons, turning knobs, or pushing sliders. However, that is not the way it all began. The first synthesizers were modular, in that they were a group of modules that each performed a separate function. For example, one module, called an oscillator, produced a waveform (sawtooth, sine, pulse, etc...) and another, the amplifier, modified the amplitude (volume) of the waveform. Each of these two modules had inputs for control voltage (CV). For the oscillator, the higher the control voltage, the higher the frequency of the wave. For the amplifier, the higher the control voltage, the larger the amplitude of the waveform was, and therefor the volume of the sound. These modules can be patched together in an almost infinite number of ways, making sound far more complex than today's synthesizers can even dream of making.

Between the years 1967 and 1981, Moog Music was designing, improving upon, and selling modules for their modular synthesizers. Although each modular system was available custom configured, there were many stock design models of the Moog modular synthesizer. Models included: 3C, 2C, 1C, 3P, 2P, 1P, 10, 12, 15, 55, 35, and C.E.M.S. (Co-ordinated Electronic Music Studio).